hen it debuted on New Year’s Day, the BBC’s eight-part drama The Serpent was met with ambivalent reviews. Do we really need another serial killer story? Does the attractiveness of its stars, Tahar Rahim and Jenna Coleman, overly glamorise a murderer and his brainwashed moll? Do there have to be quite so many flashbacks? Once you’ve peeled away the 70s fabrics and neurotic clouds of cigarette smoke, what is it actually saying? The show took a while to dispel such reservations and clarify what it was really up to. Since then, however, it’s become a word-of-mouth sensation on iPlayer, and was among the most-streamed series during the biggest-ever week for the platform. The Serpent is as much about a milieu as a man. Charles Sobhraj drugged and murdered at least a dozen people between 1975 and 1976, just after the US’s humiliating flight from Vietnam, and the show emphasises the drift and decay of the 70s. The subculture of expats and travellers in south-east Asia feels rather like Joan Didion’s 60s California, crisscrossed by lost young people trying to find themselves anew in religion, drugs, or simply unfamiliar places. In Slouching Towards Bethlehem, Didion writes of those who “drifted from city to torn city, sloughing off both the past and the future as snakes shed their skins”. The show grants the unlucky some initial moments of joy, but once they fall in with Sobhraj and his accomplices, everything they are seeking – freedom, adventure, novelty, self-discovery – turns hideously sour. It is a world in which it is far too easy to go missing and not to be missed. Sobhraj himself, born in Saigon to an Indian father and a Vietnamese mother, raised unhappily in France, is a hollow man who uses his lostness as a superpower. Rahim plays him with a sociopathic, plasticky calm, like a Ken doll costumed as a 70s gigolo. As he remakes himself as the suave gem dealer Alain Gautier, and adopts the identities of those he has robbed or murdered when he needs to travel without trace, he becomes a perversion of the 70s quest for liberation and reinvention: a man who could be from anywhere, doing anything, and who can leave a life behind at a moment’s notice. For him alone, everything is fluid. We now have terms to describe Sobhraj’s behaviour – gaslighting, coercive control – that either weren’t available or weren’t widely used in the 70s. Like Charles Manson, another predatory killer who found a loophole in the hippy dream, Sobhraj identifies fatal psychological faultlines in the people he recruits into his ersatz family. In the role, Rahim makes Coleman’s timid Canadian Catholic Marie-Andrée Leclerc bloom before he makes her rot, and gives the naive Dominique the affirmation he craves before telling him that he can never go home again. Both characters are torn between their old and new identities until they break apart, because most of us are not mentally equipped to erase ourselves and start again. Sobhraj spots more quotidian weaknesses in his victims: the simple need that someone far from home has for assistance, understanding and good company. He ruthlessly manipulates their trust and good manners. Wouldn’t it be rude to refuse a drink? Why would you suspect the friendly stranger who’s nursing you through a mysterious illness of causing it in the first place? Some older viewers, who travelled in Asia in the 70s and 80s, have noted on Twitter that The Serpent made them realise how susceptible they would have been to a man like that. Some were unsettled to realise now how vulnerable they had been, while others recalled possible near-misses with strange characters they had met along the way. The hypercompetent Sobhraj – whose ability to doctor a passport and slither out of captivity would, in another life, have made him an excellent spy – has the conman’s contempt for the conned. A man who’s thought of everything despises people who suspect nothing. In the series, as in real life, he uses valid complaints about racism and neocolonialism to justify his crimes as a kind of revenge on the embodiment of careless white privilege. In fact, he turns that privilege against them. He’s the only one who really understands Thailand and therefore knows exactly who can be fooled, seduced, bribed or intimidated. The travellers, meanwhile, seal themselves into a bubble by barely interacting with local people beyond waiters and tour guides, and thus make themselves as easy to overlook as the sex workers and drifters that other serial killers have preyed upon. Witnesses see a victim stumbling and vomiting from Sobhraj’s drugs and assume it’s just another drunk westerner, while neither the police nor the ambassadors consider it a priority to track down missing hippies who might have dropped off the map of their own accord. It’s a real-world manifestation of the sci-fi conceit in the 2018 BBC series The City and the City: two worlds that inhabit the same physical space yet are largely invisible to one another. Both series were directed by Tom Shankland. It is left to a small crew of morally dedicated amateur detectives – a junior Dutch diplomat and his wife, a jaded fixer straight out of Graham Greene, and Sobhraj’s guilt-ridden French neighbours – to cross the divide and piece the case together. Their painstaking analogue investigation has a similar appeal to the one in David Fincher’s Zodiac, and mirrors Sobhraj’s own careful process. Because it will never be understood why he did what he did, The Serpent focuses on the how. While travellers are still murdered from time to time, Sobhraj’s modus operandi would be impossible in an era of CCTV and electronic passports, when backpackers leave a social-media trail instead of reluctantly calling home every few weeks. The internet has eroded some of the distance and mystery of travel but it has also made it much harder to disappear completely. The craft behind the Serpent – from the casting to the music to the hideously suspenseful setpieces – is superb, but there are many slick, compelling shows that ultimately say nothing. What makes it unusual among serial-killer dramas is that it cares deeply about the victims and their families as well as the detectives and the murderers. Like the obsessive sleuth Herman Knippenberg, writers Richard Warlow and Toby Finlay consider it their duty to make sure the dead are remembered and honoured. Towards the end, like the gangsters in the final stretch of Goodfellas, Sobhraj becomes sloppy and decadent. His cloak of glamour is threadbare and soiled; his spell is broken; his would-be prey can finally see him for what he is. When you read the dedication in the closing seconds of the last episode, you are left in no doubt that while this empty man may be the star of the show, he is not its heart. The Serpent continues on BBC One at 9pm on Saturday, with the full series available on iPlayer now